1). When the excitation voltage and current of the generator do not exceed 1.1 times of its rated excitation current and voltage, the excitation system is ensured to operate continuously.
2). The excitation system has short time overload capability, which is greater than the short time overload capability of the generator rotor windinds.
3). The force excitation times of the excitation system shall be no less than 2 (static excitation system, even when the stator voltage drops to 80% of the rated value), the allowable force excitation time is 20s.
4). The excitation system has a high initial response characteristics, within 0.1s the excitation voltage increases to the maximum voltage and 95% of the rated voltage.
5). The response ratio of the excitation system, i.e., the voltage increase speed, shall be no less than 3.58 times/s.
6). The steady gain of the excitation system ensures that the voltage static error ratio of the generator is ≤.5%.
7). The dynamic gain the excitation system ensures that when the voltage of the generator suddenly drops, the SCR bridge opens to the maximum allowable value.
8). The regulation range of the automatic excitation regulator: in case of no load, it shall be capable of regulating smoothly within 20-110% of the rated voltage, with resolution of the setting voltage not exceeding 0.2%~0.5% of the rated voltage. In case of no load of generator, the manual voltage regulation range is 10%-130%UN.
9). The voltage frequency characteristics: when the generator no load frequency change is within ±1% and the SCR regulator can be used, the change of terminal voltage shall not exceed 0.25% of the rate value.
10). When the generator is operating under no load, the voltage regulating speed of the automatic excitation regulator may be set. The setting at delivery shall not exceed 1% rated voltage/s, and no smaller than 0.3% rated voltage/s.
11). The rotor circuit of the generator is equipped with overvoltage protection, the dispersity of operation voltage shall be no more than ±10%. The silicon parts or the SCR parts of the excitation device and other equipment may withstand the operating conditons such as DC side short circuit fault and asynchronous operation of generator.
12). The forced outage rate of generator caused by fault of excitation system shall be no more than 0.25 time/year, the forced clearance rate of excitation system shall not exceed 0.1%.
13). The availability of AVR (including PSS) shall not be lower than 99.9%.
14). The exciation system shall meet the requirement of 125% of terminal voltage in case of turbine generator short circuit and no loat test.
2.2 Operation and Adjustment of Excitation System
The UNITROL5000 excitation system is a complete set installed in power plant. The generator static excitation system consists of 9 panels, arranged in a line by the generator at turbine house 13.7m platform. The arrangement of the panels is as shown in Table 2-1 (front view):
Table 2-1 Arrangement of UNITROL5000 excitation system panels
ＡＶ Ｒ panel Deexcitation panel DC outgoing line panel Rectifier panel Rectifier panel Rectifier panel Rectifier panel Rectifier panel AC excitation incoming line panel The UNITROL5000 excitation system has the following main control methods:
a. Remote control by key pad orders in the control room. These orders are given through the excitation system in binary signals.
b. Remote control by scree monitor control orders in the control room. These orders are given through the excitation system in binary signals or through the Field bus.
c. Local control by local control unit (local control panel) integrated in the excitation system.
In normal conditions the excitation system is operated by the control system through remote control. The local control panel installed on the front panel of the exciation system is only optional in case of commissioning, test or emergency. The operators must be familiar with the design of system control and display elements, the functions of the orders of the excitation system as well as the use of control and display units.
2.2.1 Control and display unit
(feedback indication) shows whether the feedback indication is displayed in the control room: Table 2-2 List of available remote and local control orders
Order Remote Local Feedback
indication
Excitation circuit switch on Χ Χ Χ
Excitation circuit switch off Χ Χ Χ
Excitation on Χ Χ Χ Excitation off Χ Χ Χ Channel 1 in operation Χ Χ Χ Channel 2 in operation Χ Χ Χ Operation mode-auto Χ Χ Operation mode-manual Χ Χ
Operating regulator given point up
Χ Χ Max.
Operating regulator given point down
Χ Χ Max.
Reactive power regulator in service
Χ Χ Χ
Reactive power regulator out of service Χ Χ Χ PSS in service Χ Χ PSS out of service Χ Χ Control mode...Local Χ Χ Control mode...Remote Χ
Test of indicator lamp Χ
Release Χ
Excitation switch on Χ Χ
Excitation switch off Χ Χ
The shaded area in the above table gives the local control orders, indicating that they are only effective when the ENABLE key is pressed on the local control panel. Before the excitation system is put into service, it must be ensured that all the required power supplies are in place to maintain safe startup, and the following inspections must be done:
1). Maintenance of the system is completed
2). The control and power cabinets are ready and properly locked
3). The generator delivers no load and the temporary earthing wires are removed 4). The control power supply of the deexcitation switch and the power supply of he regulator are energized
5). There are no alarm and fault signals
6). The excitation system is switched to remote control mode 7). The excitation system is switched to automatic operation mode
8). The generator reaches rated speed (check the speed shown on the display instrument)